H-Mode Accelerating Structures with PMQ Beam Focusing

TL;DR

This paper presents a novel high-efficiency RF accelerating structure combining H-mode resonators with permanent-magnet quadrupoles for improved beam focusing and size reduction in ion accelerators.

Contribution

It introduces a new IH-PMQ structure with significantly higher shunt impedance and smaller transverse size, supported by comprehensive modeling and experimental validation.

Findings

Shunt impedance 10-20 times higher than conventional linacs

Transverse size reduced by 4-5 times

Good agreement between measurements and simulations

Abstract

We have developed high-efficiency normal-conducting RF accelerating structures by combining H-mode resonator cavities and a transverse beam focusing by permanent-magnet quadrupoles (PMQ), for beam velocities in the range of a few percent of the speed of light. The shunt impedance of inter-digital H-mode (IH-PMQ) structures is 10-20 times higher than that of a conventional drift-tube linac, while the transverse size is 4-5 times smaller. Results of the combined 3-D modeling - electromagnetic computations, multi-particle beam-dynamics simulations with high currents, and thermal-stress analysis - for an IH-PMQ accelerator tank are presented. The accelerating field profile in the tank is tuned to provide the best propagation of a 50-mA deuteron beam using coupled iterations of electromagnetic and beam-dynamics modeling. Measurements of a cold model of the IH-PMQ tank show a good agreement with the calculations. H-PMQ accelerating structures following a short RFQ can be used both in the front end of ion linacs or in stand-alone applications.